Homeowner guide · Water heaters
Tank vs. tankless water heaters: what the Energy Department says
According to the U.S. Department of Energy, a tankless water heater can be 24 to 34 percent more energy efficient than a tank for a home using 41 gallons of hot water a day or less, and usually lasts longer. But it delivers a limited flow, which matters for busy households. Here are the numbers.
Key takeaways
The short version
- Tankless units can be 24 to 34 percent more efficient for homes using 41 gallons a day or less, DOE says.
- For heavy users, around 86 gallons a day, the gain drops to 8 to 14 percent.
- Tankless heaters typically supply 2 to 5 gallons of hot water per minute.
- DOE says most tankless units last more than 20 years; storage tanks last 10 to 15.
- Even the largest gas tankless model cannot supply several uses at once in a large household.
The numbers side by side
| Measure | Tankless | Storage tank |
|---|---|---|
| Efficiency, home using 41 gallons a day or less | 24 to 34 percent more efficient than a tank | Baseline |
| Efficiency, home using about 86 gallons a day | 8 to 14 percent more efficient than a tank | Baseline |
| Hot water flow | Typically 2 to 5 gallons per minute | Limited by the tank’s stored volume |
| Life expectancy | More than 20 years for most units | 10 to 15 years |
Source: U.S. Department of Energy. The “baseline” and tank flow rows are our framing for comparison, not DOE figures.
Where tankless falls short
DOE says even the largest gas-fired tankless model cannot supply enough hot water for simultaneous, multiple uses in large households (U.S. Department of Energy). If your mornings involve two showers and a dishwasher at once, that limit matters more than the efficiency figure.
Gas units can also waste energy if they have a standing pilot light. DOE suggests looking for a model with an intermittent ignition device instead.
Which fits your household
Tankless tends to fit
Smaller households, lighter hot water use, and owners planning to stay long enough to benefit from the longer life.
A tank tends to fit
Larger households that run several fixtures at once and want a lower upfront change from what is already installed.
These are our general recommendations based on the DOE figures above. Upfront and installation costs vary by home, and DOE’s page does not give a single price for either type.
Why water heating is worth getting right
Montana’s weatherization program, run with Montana State University Extension, says water heating can account for up to 20 percent of a home’s energy use (Montana Weatherization / MSU Extension). Whichever type you choose, sizing it to your household matters as much as the type.
When to call
Replacing a water heater this winter?
We install tank and tankless water heaters for homes in Wayne, Strafford, Paoli, Chesterbrook, Berwyn and Devon, and we size them to how your household uses hot water. Call (610) 788-0042.
Frequently asked questions
Tank vs. tankless questions
Answers by John, Tredyffrin Easttown Plumber.
Is a tankless water heater more efficient than a tank?
DOE says tankless units can be 24 to 34 percent more efficient for homes using 41 gallons of hot water a day or less, and 8 to 14 percent more efficient for homes using about 86 gallons a day.
How long does a tankless water heater last?
DOE says most tankless water heaters have a life expectancy of more than 20 years, compared with 10 to 15 years for storage tanks.
How much hot water can a tankless heater supply?
DOE says tankless heaters typically provide 2 to 5 gallons of hot water per minute.
Can a tankless heater run two showers at once?
It depends on the unit and the demand. DOE says even the largest gas-fired model cannot supply enough hot water for simultaneous, multiple uses in large households.
How much does a tankless water heater cost to install?
Not found. DOE’s tankless page does not give a single installed price; costs depend on the home.
Sources
Where these facts come from
Every figure and rule in this guide comes from the public sources below. Rules and fees can change, so confirm with the source before you act.
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Our service area
Plumbing across Tredyffrin Township, PA
Tredyffrin Easttown Plumber serves every neighborhood in Tredyffrin Township, including Wayne, Strafford, Chesterbrook, Paoli, Berwyn, Devon, Daylesford, and Howellville, plus neighboring Easttown Township. Our office is at 217 Conestoga Rd, Suite 10, Wayne, PA 19087.
